There is currently no commercially available and clinically successful treatment for scapholunate interosseous ligament rupture, the latter leading to the development of hand-wrist osteoarthritis. We have created a novel biodegradable implant which fixed the dissociated scaphoid and lunate bones and encourages regeneration of the ruptured native ligament. To determine if scaphoid and lunate kinematics in cadaveric specimens were maintained during robotic manipulation, when comparing the native wrist with intact ligament and when the implant was installed. Ten cadaveric experiments were performed with identical conditions, except for implant geometry that was personalised to the anatomy of each cadaveric specimen. Each cadaveric arm was mounted upright in a six degrees of freedom robot using k-wires drilled through the radius, ulna, and metacarpals. Infrared markers were attached to scaphoid, lunate, radius, and 3rd metacarpal. Cadaveric specimens were robotically manipulated through flexion-extension and ulnar-radial deviation by ±40° and ±30°, respectively. The cadaveric scaphoid and lunate kinematics were examined with 1) intact native ligament, 2) severed ligament, 3) and installed implant. Digital wrist models were generated from computed tomography scans and included implant geometry, orientation, and location. Motion data were filtered and aligned relative to neutral wrist in the digital models of each specimen using anatomical landmarks. Implant insertion points in the scaphoid and lunate over time were then calculated using digital models, marker data, and inverse kinematics. Root mean squared distance was compared between severed and implant configurations, relative to intact. Preliminary data from five cadaveric specimens indicate that the implant reduced distance between scaphoid and lunate compared to severed configuration for all but three trials. Preliminary results indicate our novel implant reduced scapho-lunate gap caused by ligament transection. Future analysis will reveal if the implant can achieve wrist kinematics similar to the native intact wrist

This study aims to create a novel computational workflow for frontal plane laxity evaluation which combines a rigid body knee joint model with a non-linear implicit finite-element model wherein collateral ligaments are anisotropically modelled using subject-specific, experimentally calibrated Holzpfel-Gasser-Ogden (HGO) models. The framework was developed based on CT and MRI data of three cadaveric post-TKA knees. Bones were segmented from CT-scans and modelled as rigid bodies in a multibody dynamics simulation software (MSC Adams/view, MSC Software, USA). Medial collateral and lateral collateral ligaments were segmented based on MRI-scans and are modelled as finite elements using the HGO model in Abaqus (Simulia, USA). All specimens were submitted varus/valgus loading (0-10Nm) while being rigidly fixed on a testing bench to prevent knee flexion. In subsequent computer simulations of the experimental testing, rigid bodies kinematics and the associated soft-tissue force response were computed at each time step. Ligament properties were optimised using a gradient descent approach by minimising the error between the experimental and simulation-based kinematic response to the applied varus/valgus loads. For comparison, a second model was defined wherein collateral ligaments were modelled as nonlinear no-compression spring elements using the Blankevoort formulation. Models with subject-specific, experimentally calibrated HGO representations of the collateral ligaments demonstrated smaller root mean square errors in terms of kinematics (0.7900° +/− 0.4081°) than models integrating a Blankevoort representation (1.4704° +/− 0.8007°). A novel computational workflow integrating subject-specific, experimentally calibrated HGO predicted post-TKA frontal-plane knee joint laxity with clinically applicable accuracy. Generally, errors in terms of tibial rotation were higher and might be further reduced by increasing the interaction nodes between the rigid body model and the finite element software. Future work should investigate the accuracy of resulting models for simulating unseen activities of daily living

Abstract. Objectives. Conventional approaches (including Tobit) do not accurately account for ceiling effects in PROMs nor give uncertainty estimates. Here, a classifier neural network was used to estimate postoperative PROMs prior to surgery and compared with conventional methods. The Oxford Knee Score (OKS) and the Oxford Hip Score (OHS) were estimated with separate models. Methods. English NJR data from 2009 to 2018 was used, with 278.655 knee and 249.634 hip replacements. For both OKS and OHS estimations, the input variables included age, BMI, surgery date, sex, ASA, thromboprophylaxis, anaesthetic and preoperative PROMs responses. Bearing, fixation, head size and approach were also included for OHS and knee type for OKS estimation. A classifier neural network (NN) was compared with linear or Tobit regression, XGB and regression NN. The performance metrics were the root mean square error (RMSE), maximum absolute error (MAE) and area under curve (AUC). 95% confidence intervals were computed using 5-fold cross-validation. Results. The classifier NN and regression NN had the best RMSE, both with the same scores of 8.59±0.04 for knee and 7.88±0.04 for hip. The classifier NN had the best MAE, with 6.73±0.03 for knee and 5.73±0.03 for hip. The Tobit model was second, with 6.86±0.03 for knee and 6.00±0.01 for hip. The classifier NN had the best AUC, with (68.7±0.4)% for knee and (73.9±0.3)% for hip. The regression NN was second, with (67.1±0.3)% for knee and (71.1±0.4)% for hip. The Tobit model had the best AUC among conventional approaches, with (66.8±0.3)% for knee and (71.0±0.4)% for hip. Conclusions. The proposed model resulted in an improvement from the current state-of-the-art. Additionally, it estimates the full probability distribution of the postoperative PROMs, making it possible to know not only the estimated value but also its uncertainty

Abstract. Objectives. Total hip arthroplasty (THA) procedures are physically demanding for surgeons. Repetitive mallet swings to impact a surgical handle (impactions), can lead to muscle fatigue, discomfort and injuries. The use of an automated surgical hammer may reduce fatigue and increase surgical efficiency. The aim of this study was to develop a method to quantify user's performance, by recording surface electromyography (sEMG), for automated and manual impactions. Methods. sEMG signals were recorded from eight muscle compartments (arm and back muscles) of an orthopaedic surgeon during repetitions of manual and automated impaction tasks, replicating femoral canal preparation (broaching) during a THA. Each task was repeated, randomly, four times manually and four times with the automated impaction device. The mechanical outcomes (broaching efficiency and broach advancement) were quantified by tracking the kinematics of the surgical instrumentation. Root mean square (RMS) values and median frequency (MDF) were calculated for each task to, respectively, investigate which muscles were mostly involved (higher RMS) in each task and to quantify the decrease in MDF, which is an indicator of muscle fatigue. Results. RMS for arm muscles was significantly higher (p-value=0.002) during manual impactions than during automated impactions and muscle fatigue was significantly reduced (p-value=0.011), for the same muscles, when the same tasks were performed with the automated surgical hammer. The time required to achieve the same mechanical outcome, in terms of broaching efficiency and broach advancement, was significantly reduced with the automated surgical hammer (p=0.019). Conclusions. Results from this study showed how with this methodology it was possible to discern muscle performance and fatigue, between impaction modalities. Moreover, the reduction in exposure time to automated impactions, could be a factor in muscle fatigue decrease. These results could therefore provide useful insights into the study of surgical ergonomic improvements, to reduce surgeons muscle fatigue and, potentially, injuries. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Abstract. Objectives. Develop a methodology to assess the long term mechanical behavior of intervertebral discs by utilizing novel sequential state testing. Methods. Bovine functional spinal units were sequentially mechanically tested in (1) native (n=8), (2) degenerated (n=4), and (3) treated states (n=4). At stage (2), artificial degeneration was created using rapid enzymatic degeneration, followed by a 24 hour hold period under static load at 42°C. At stage (3), nucleus augmentation treatments were injected with a hydrogel or a ‘sham’ (water, chondroitin sulfate) injection. The mechanical protocol employed applied a static load hold period followed by cyclic compressive loading between ∼350 and 750 N at 1 Hz. 1000 cycles were applied at each stage, and the final test on each specimen was extended up to 20000 cycles. To verify if test time can be reduced, functions were fitted using stiffness data up to 100, 1000, 2500, 5000, 10000 and 20000 cycles. Linear regression for the native specimens comparing the stiffness at various cycles to the stiffness at 20000 cycles was completed. Results. Independent of the disc state, as the number of cycles increased, the hysteresis decreased and the stiffness increased. The degenerated specimen stiffness was greater than the healthy and treated stiffness and the degenerate hysteresis loops were smaller. A mathematical model was found to successfully predict the high cycle behaviour of the disc reaching a root mean squared (RMS) error below 10% when using 5000 or more cycles. The linear regression gave a RMS error below 7.5% at 1000 cycles. Conclusions. A method was developed to consistently determine intervertebral disc mechanics through sequential testing. A shortened cyclic testing period was shown to be viable as a method to reduce preliminary test time for novel hydrogels, compared to currently literature. The methodology permits rapid preliminary assessment of intervertebral disc mechanics and treatments. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

The angle of acetabular inclination is an important measurement in total hip replacement (THR) procedures. Determining the acetabular component orientation intra-operatively remains a challenge. An increasing number of innovators have described techniques and devices to achieve it. This paper describes a mechanical inclinometer design to measure intra-operative acetabular cup inclination. Then, the mechanical device is tested to determine its accuracy. The aim was to design an inclinometer to measure inclination without existing instrumentation modification. The device was designed to meet the following criteria: 1. measure inclination with acceptable accuracy (+/− 5o); 2. easy to use intra-operatively (handling & visualization); 3. adaptable and useable with majority of instrumentation kits without modification; 4. sterilizable by all methods; 5. robust/reusable. The prototype device was drafted by computer aided design (CAD) software. Then a prototype was constructed using a 3D printer to establish the final format. The final device was CNC machined from SAE 304 stainless steel. The design uses an eccentrically weighted flywheel mounted on two W16002-2RS ball bearings pressed into symmetrical housing components. The weighted wheel is engraved with calibrated markings relative to its mass centre. Device functioning is dependent on gravity maintaining the weighted wheel in a fixed orientation while the housing can adapt to the calibration allowing for determining the corresponding measurement. The prototype device accuracy was compared to a digital device. A digital protractor was used to create an angle. The mechanical inclinometer (user blinded to digital reading) was used to determine the angle and compared to the digital reading. The accuracy of the device compared to the standard freehand technique was assessed using a saw bone pelvis fixed in a lateral decubitus position. 18 surgeons (6 expert, 6 intermediate, 6 novice) were asked to place an uncemented acetabular cup in a saw bone pelvis to a target of 40 degrees. First freehand then using the inclinometer. The inclination was determined using a custom-built inertial measurement unit with the user blinded to the result. Comparison between the mechanical and digital devices showed that the mechanical device had an average error of −0.2, a standard deviation of 1.5, and range −3.3 to 2.6. The average root mean square error was 1.1 with a standard deviation of 0.9. Comparison of the inclinometer to the freehand technique showed that with the freehand component placement 50% of the surgeons were outside the acceptable range of 35–45 degrees. The use of the inclinometer resulted all participants to achieve placement within the acceptable range. It was noted that expert surgeons were more accurate at achieving the target inclination when compared to less experienced surgeons. This work demonstrates that the design and initial testing of a mechanical inclinometer is suitable for use in determining the acetabular cup inclination in THR. Experimental testing showed that the device is accurate to within acceptable limits and reliably improved the accuracy of uncemented cup implantation in all surgeons

Anterior-posterior (AP) x-rays are routinely taken following total hip replacement to assess placement and orientation of implanted components. Pelvic orientation at the time of an AP x-ray can influence projected implant orientation. 1. However, the extent of pelvic orientation varies between patients. 2. Without compensation for patient specific pelvic orientation, misleading measurements for implant orientation may be obtained. These measurements are used as indicators for post-operative dislocation stability and range of motion. Errors in which could result in differences between expectations and the true outcome achieved. The aim of this research was to develop a tool that could be utilised to determine pelvic orientation from an AP x-ray. An algorithm based on comparing projections of a statistical shape model of the pelvis (n=20) with the target X-ray was developed in MATLAB. For each iteration, the average shape was adjusted, rotated (to account for patient-specific pelvic orientation), projected onto a 2D plane, and the simulated outline determined. With respect to rotation, the pelvis was allowed to rotate about its transverse axis (pelvic flexion/extension) and anterior-posterior axis (pelvic adduction/abduction). Minimum root mean square error between the outline of the pelvis from the X-ray and the projected shape model outline was used to select final values for flexion and adduction. To test the algorithm, virtual X-rays (n=6) of different pelvis in known orientations were created using the algorithm described by Freud et al. 3. The true pelvic orientation for each case was randomly generated. Angular error was defined as the difference between the true pelvic orientation and that selected by the algorithm. Initial testing has exhibited similar accuracy in determining true pelvic flexion (x̄error = 2.74°, σerror=±2.21°) and true pelvic adduction (x̄error = 2.38°, σerror=±1.76°). For both pelvic flexion and adduction the maximum angular error observed was 5.62°. The minimum angular error for pelvic flexion was 0.37°, whilst for pelvic adduction it was 1.08°. Although the algorithm is still under development, the low mean, maximum, and standard deviations of error from initial testing indicate the approach is promising. Ongoing work will involve the use of additional landmarks for registration and training shapes to improve the shape model. This tool will allow surgeons to more accurately determine true acetabular orientation relative to the pelvis without the use of additional x-ray views or CT scans. In turn, this will help improve diagnoses of post-operative range of motion and dislocation stability

Image-free navigation technology relies heavily on the surgeon carefully registering bony anatomical landmarks, a critical step in achieving accurate registration which affects the entire procedure. Currently this step may depend on placing a pointer superficially, with soft-tissue and skin obscuring these bony landmarks. We report initial results of using newly developed experimental software which automatically recognises the bone soft-tissue interface. This is the first critical step in development of automatic computer generation of the bone surface topography from ultrasound scanning. Individual 2D ultrasound images (n=651) of the anterior femoral condyles and trochlear notch were used. Images were taken from 29 volunteers (20 male, 9 female). The software extracted bone-soft tissue interface by a two-step method based on a gradient evaluation and the elimination of false-positives with a graph closure. The trochlear notch was automatically defined by geometrical modelisation. Coordinates of both bone interface and trochlear notch position for each separate image were compared to a separate analysis performed manually by a single investigator. Error was calculated using root mean squared (RMS). Median error (RMS) in locating bone soft-tissue interface was 0.67 mm, (mean 0.93 mm, SD 0.84 mm). Median error for trochlear notch topography was 1.01mm, (mean 1.41 mm, SD 1.37 mm). Bone soft-tissue interface can be accurately defined and displayed by this software. Direct visualisation of critical bony landmarks could replace the current comparatively subjective placement of a pointer on superficial tissues. This has powerful application in both non-invasive and surgical computer-assisted acquisition of knee kinematics, and may have further applications in orthopaedic surgery

Introduction. Knowledge of knee kinetics and kinematics contributes to our understanding of the patho-mechanics of knee pathology and rehabilitation and a mobile system for use in the clinic is desirable. We set out to assess validity and reliability of ambulatory Inertial Motion Unit (IMU) Sensors (Pegasus¯) against an established optoelectronic system (CODA¯). Pegasus¯ uses inertial sensors placed on subjects' thighs and lower leg segments to directly measure orientation of these segments with respect to gravity. CODA¯) models the position of joint centres based on tracked positions of optical markers placed on a subject, providing 3D kinematics of the subject's hips, knees and ankles in all three planes. Methods. Intra observer reliability of the Pegasus¯ system was tested on 6 volunteers (4 male; 2 female) with no previous lower limb or knee pathology. IMU's were placed on the long axis of the lateral aspects of both thighs and lower leg segments. A test re-test protocol was used with sagittal data angle collected around a standard circuit. Inter-observer reliability was tested by placement of IMU's by 5 different testers on a single volunteer. To test validity, we collected simultaneous sagittal knee angle data from Pegasus¯ and CODA¯ in two subjects. The presence of IMU's did not compromise positioning of optical markers. Results. Analysis of triplicate measurements showed that intra-observer error is +/− 5°. Inter-observer difference in measurements varied from 3° to 20° absolute values. Positional error of the Pegasus¯ IMU's was significant in comparison to CODA¯, with absolute offsets in knee angles typically of 10° to 25°. Range of motion differences between the two systems calculated as root mean square (rms) difference of the zero meaned signals were 3.8°-4.8°. Conclusion. The Pegasus¯ system is useful in ambulatory measurement of the range of knee motion in the sagittal plane. In the current configuration there was poor intra and inter-observer reliability possibly related to positional error using the Pegasus¯ system and may be due to fixation method, operator factors, body shape and variability of clothing. Recommendations have been made to the manufacturer

Weight-bearing is a known stimulus for bone remodelling and a reduction in weight-bearing is associated with reduced bone mineral density (BMD) in affected limbs post lower limb fracture. This study investigated short and long-term precision of a method for measuring relative left/right weight-bearing using two sets of identical calibrated scales. The effect of imbalance on BMD at the hip and on lower limb lean tissue mass (LLTM) was also assessed. 46 postmenopausal women, with no history of leg or ankle fracture, were measured three times whilst standing astride two scales (Seca, Germany). 34 of the participants were re-measured after 6 months by the same method. Bilateral hip and total body dual x-ray absorptiometry measurements were performed using a GE Lunar Prodigy (Bedford, MA). Precision errors in weight-bearing measures were calculated using the root mean square coefficient of variation (RMSCV%). The correlations at the first visit between left/right differences in weight-bearing and differences in BMD and LLTM were calculated. The short-term RMSCV% for left and right weights were 4.20% and 4.25% respectively and the long-term RMSCV% were 6.91% and 6.90%. Differences in left/right weight-bearing ranged from 0 to 24% (SD 8.63%) at visit 1 and 0 to 30% (SD 10.71%) at visit 2. Using data from visit 1, the relationship between hip BMD differences and left/right weight-bearing differences were investigated, with no significant correlations found. However, a weak, but statistically significant correlation of r=0.35 (p=0.02) was found for differences in LLTM and left/right weight-bearing differences. In conclusion, left/right weight-bearing measured using two scales is a precise method for evaluating differences in weight-bearing in the short and long-term. Differences in left/right weight-bearing in this population varied by up to 30%. Participants showed a high degree of consistency in their long-term balance in a natural standing posture. Inequalities in left/right weight-bearing did not correlate significantly with BMD at the hip, but demonstrated a weak but statistically significant correlation with lean tissue mass

The human acetabulofemoral joint is commonly modelled as a pure ball-and-socket joint, but there has been no quantitative assessment of this assumption in the literature. Our aim was to test the limits and validity of this hypothesis. We performed experiments on four adult cadavers. Cortical pins, each equipped with a marker cluster, were implanted in the pelvis and the femur. Movements were recorded using stereophotogrammetry while an operator rotated the cadaver’s acetabulofemoral joint, exploiting the widest possible range of movement. The functional consistency of the acetabulofemoral joint as a pure spherical joint was assessed by comparing the magnitude of the translations of the hip joint centre as obtained on cadavers, with the centre of rotation of two metal segments linked through a perfectly spherical hinge. The results showed that the radii of the spheres containing 95% of the positions of the estimated centres of rotation were separated by less than 1 mm for both the acetabulofemoral joint and the mechanical spherical hinge.

Therefore, the acetabulofemoral joint can be modelled as a spherical joint within the considered range of movement (flexion/extension 20° to 70°; abduction/adduction 0° to 45°; internal/external rotation 0° to 30°).

Our aim was to investigate the relationship between urinary excretion of deoxypyridinoline (DPD) as a marker of bone resorption, and Perthes’ disease. There were 39 children with Perthes’ disease in the florid stage who collected first-morning urine samples at regular intervals of at least three months. The level of urinary DPD was analysed by chemiluminescence immunoassay and was correlated with the radiological stage of the disease as classified by Waldenström, and the severity of epiphyseal involvement according to the classification systems of Catterall and Herring. The urinary DPD levels of a group of 44 healthy children were used as a control.

The median urinary DPD/creatinine (CREA) ratio was significantly reduced (p < 0.0001) in the condensation stage and increased to slightly elevated values at the final stage (p = 0.05) when compared with that of the control group. Herring-C patients showed significantly lower median DPD/CREA ratios than Herring-B patients (p = 0.03). The significantly decreased median DPD/CREA ratio in early Perthes’ disease indicated a reduced bone turnover and supports the theory of a systemic aetiology. Urinary levels of DPD may therefore be used to monitor the course of Perthes’ disease.